FIGS. 1 and 2 show a conventional prop 10 for supporting moldboards. The prop 10 includes an outer tube 12, a threaded tube 13 fixed at a top end of the outer tube 12 and an inner tube 15 telescopically fitted in the threaded tube 13 and the outer tube 12. The threaded tube 13 is formed with a pair of axial slots 14. The inner tube 15 is formed with several pairs of pinholes 16 arranged at equal intervals. A locating nut 17 is adjustably screwed on the threaded tube 13. An insertion pin 18 is passed through the slots 14 of the threaded tube 13 and inserted into one pair of pinholes of the inner tube 15. In use, the inner and outer tubes 15, 12 are adjusted to a necessary length and then the insertion pin 18 is inserted through the slots 14 of the threaded tube 13 into one pair pinholes 16 of the inner tube 15. The insertion pin 18 is supported by the locating nut 17. By means of turning the nut 17, the length of the inner tube 15 extending out of the outer tube 12 can be adjusted, whereby the prop serves to support a moldboard.
The conventional prop 10 has some shortcomings as follows:
First, the length of the prop is adjusted by means of turning the locating nut 17. It takes much time to complete such procedure. Therefore, a user can hardly quickly conveniently adjust the length of the prop to a necessary length.
Second, such prop 10 is designed for bearing pressure only. Therefore, the prop 10 cannot bear pulling force. In the case that an axial pressure is applied to the prop 10, the inner tube 15 is supported by the nut 17 without being retracted into the outer tube 12. However, in the case that an axial pulling force is applied to the prop, the inner tube will slide and displace. Accordingly, the prop can only bear one-way action force, that is, the axial pressure. Therefore, such prop is inapplicable to the situation of bidirectional action force so that the application range of such prop is narrowed.
U.S. Pat. No. 6,467,741 entitled “steel prop capable of bearing bidirectional applied force” of this applicant discloses a prop capable of bearing bidirectional action force. However, it is relatively inconvenient to operate such prop. In addition, the prop has a relatively complicated structure.